support calls on opaque types :<

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -204,7 +204,7 @@ where
                         //
                         // Only goals proven via the trait solver should be region dependent.
                         Certainty::Yes => {}
-                        Certainty::Maybe(_) => {
+                        Certainty::Maybe { .. } => {
                             self.obligations.register(obligation, None);
                         }
                     }
@@ -258,7 +258,7 @@ where
                             infcx.push_hir_typeck_potentially_region_dependent_goal(obligation);
                         }
                     }
-                    Certainty::Maybe(_) => self.obligations.register(obligation, stalled_on),
+                    Certainty::Maybe { .. } => self.obligations.register(obligation, stalled_on),
                 }
             }
 

compiler/rustc_trait_selection/src/solve/fulfill/derive_errors.rs

@@ -95,15 +95,17 @@ pub(super) fn fulfillment_error_for_stalled<'tcx>(
             root_obligation.cause.span,
             None,
         ) {
-            Ok(GoalEvaluation { certainty: Certainty::Maybe(MaybeCause::Ambiguity), .. }) => {
-                (FulfillmentErrorCode::Ambiguity { overflow: None }, true)
-            }
+            Ok(GoalEvaluation {
+                certainty: Certainty::Maybe { cause: MaybeCause::Ambiguity, .. },
+                ..
+            }) => (FulfillmentErrorCode::Ambiguity { overflow: None }, true),
             Ok(GoalEvaluation {
                 certainty:
-                    Certainty::Maybe(MaybeCause::Overflow {
-                        suggest_increasing_limit,
-                        keep_constraints: _,
-                    }),
+                    Certainty::Maybe {
+                        cause:
+                            MaybeCause::Overflow { suggest_increasing_limit, keep_constraints: _ },
+                        ..
+                    },
                 ..
             }) => (
                 FulfillmentErrorCode::Ambiguity { overflow: Some(suggest_increasing_limit) },
@@ -266,7 +268,8 @@ impl<'tcx> BestObligation<'tcx> {
             );
             // Skip nested goals that aren't the *reason* for our goal's failure.
             match (self.consider_ambiguities, nested_goal.result()) {
-                (true, Ok(Certainty::Maybe(MaybeCause::Ambiguity))) | (false, Err(_)) => {}
+                (true, Ok(Certainty::Maybe { cause: MaybeCause::Ambiguity, .. }))
+                | (false, Err(_)) => {}
                 _ => continue,
             }
 
@@ -407,7 +410,8 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
         let tcx = goal.infcx().tcx;
         // Skip goals that aren't the *reason* for our goal's failure.
         match (self.consider_ambiguities, goal.result()) {
-            (true, Ok(Certainty::Maybe(MaybeCause::Ambiguity))) | (false, Err(_)) => {}
+            (true, Ok(Certainty::Maybe { cause: MaybeCause::Ambiguity, .. })) | (false, Err(_)) => {
+            }
             _ => return ControlFlow::Continue(()),
         }
 

compiler/rustc_trait_selection/src/solve/inspect/analyse.rs

@@ -332,7 +332,7 @@ impl<'a, 'tcx> InspectGoal<'a, 'tcx> {
                 inspect::ProbeStep::MakeCanonicalResponse { shallow_certainty: c } => {
                     assert_matches!(
                         shallow_certainty.replace(c),
-                        None | Some(Certainty::Maybe(MaybeCause::Ambiguity))
+                        None | Some(Certainty::Maybe { cause: MaybeCause::Ambiguity, .. })
                     );
                 }
                 inspect::ProbeStep::NestedProbe(ref probe) => {

compiler/rustc_trait_selection/src/solve/select.rs

@@ -62,7 +62,7 @@ impl<'tcx> inspect::ProofTreeVisitor<'tcx> for Select {
 
         // Don't winnow until `Certainty::Yes` -- we don't need to winnow until
         // codegen, and only on the good path.
-        if matches!(goal.result().unwrap(), Certainty::Maybe(..)) {
+        if matches!(goal.result().unwrap(), Certainty::Maybe { .. }) {
             return ControlFlow::Break(Ok(None));
         }
 
@@ -95,7 +95,7 @@ fn candidate_should_be_dropped_in_favor_of<'tcx>(
 ) -> bool {
     // Don't winnow until `Certainty::Yes` -- we don't need to winnow until
     // codegen, and only on the good path.
-    if matches!(other.result().unwrap(), Certainty::Maybe(..)) {
+    if matches!(other.result().unwrap(), Certainty::Maybe { .. }) {
         return false;
     }
 
@@ -143,13 +143,13 @@ fn to_selection<'tcx>(
     span: Span,
     cand: inspect::InspectCandidate<'_, 'tcx>,
 ) -> Option<Selection<'tcx>> {
-    if let Certainty::Maybe(..) = cand.shallow_certainty() {
+    if let Certainty::Maybe { .. } = cand.shallow_certainty() {
         return None;
     }
 
     let nested = match cand.result().expect("expected positive result") {
         Certainty::Yes => thin_vec![],
-        Certainty::Maybe(_) => cand
+        Certainty::Maybe { .. } => cand
             .instantiate_nested_goals(span)
             .into_iter()
             .map(|nested| {